Formation Theory Parameters
Solar System Formation
Understanding the Seasons
Time & Its Measurement
& Lunar Eclipses
A Possible Sequence of Events
for the Formation of the Solar System
- Gas and dust nebula collapses:
- Time: Began about five billion years ago
- Duration: 10 million years
- An interstellar cloud of gas and dust, approximately 50,000
AU in diameter, began to collapse gravitationally. Its mass may
have been a few thousand solar masses. The cloud fragmented and
one area with at least 1.1 to 2.0 solar masses, continued to collapse.
Several mechanisms could have initiated such an event.
- Collection of mass from the explosion of a
supernova. As the shock wave from the supernova event
moves through space a region of higher density is generated
immediately in back of the wave front.
- Magnetic fields which originate in the
center of a galaxy give rise to shock fronts which move through
the medium at lower velocities than the medium itself. As
charged particles come in contact with the field lines, they
are slowed, collecting matter which creates the necessary
densities which generate stars.
- O B Associations: Hot luminous blue supergiant
stars create interstellar winds from their tremendous outpourings
of radiation which compress new material to form new stars,
etc. This occurs in large, interstellar clouds of hydrogen.
- Pressure and density increased. Rotation of the nebula
increased. The cloud formed a disk about 60 AU across and about
one AU thick. Temperatures rose more rapidly near the center where
the density and opacity were greatest. The center of the cloud may
have been about 2000 K (3000 °F), while the edge remained cold at
about 100 K (-300 °F). Dust vaporized near the center, and atoms became
ionized creating a magnetic field which permeated the contracting
- Transfer of angular momentum
- Duration: Perhaps as short as a few thousand years
- Magnetohydrodynamic effect transfers the sun's spin away
from the inner to the outer solar system (Alfven-1954).
- Early contracting sun had a strong magnetic field.
- Area immediately surrounding the sun was composed
of ionized particles. Charged particles interacted with the
magnetic field so that they spiraled outward along the magnetic
lines of force. These magnetic lines returned to the sun,
trapping the ions.
- The sun was rotating faster than the ions in
- The magnetic field lines of the sun, sweeping
through the ions tended to accelerate the cloud, increasing
its rotational velocity at the expense of the sun's spin.
Angular momentum was transferred away from the sun.
- The drag effect of the cloud against the sun
also tended to decrease the rotational velocity of the sun.
- Differences in composition between the inner
and outer planets can be accounted for.
- The magnetic field of the sun tended to cause more positively
charged ions (especially the volatiles) to orbit around
the forming star, thus helping to segregate the volatiles
from the more refractory materials which condensed first
in the cooling nebula. The condensed refractories such
as iron, nickel, and silicate grains would no longer have
been affected by the solar magnetic field, because they
would have been neutral. This matter would have collected
into the more refractory terrestrial planets, i.e., the
inner solar system.
- The volatiles would have remained charged and thus they
would have been affected by the sun's magnetic field.
These materials would have spiraled away from the sun
along the sun's magnetic field lines and condensed much
farther away in the cooler regions where the Jovian planets
orbit the sun today.
- The basic problem of the Magnetohydrodynamic
Effect lies with the assumption that the sun's magnetic field
strength would have had to have been 150,000 times stronger
than it is today. Presently the field strength of the sun
is approximately two gauss, four to six times that of the
earth's field strength.
- Formation of grains and planetesimals
- Grains condensed with the composition dependent upon
the temperature of the immediate environment. Generally, the denser
terrestrial materials formed nearer to the sun, while icy materials
condensed farther away.
- Grains collided to form planetesimals, small bodies ranging
in size from millimeters to 10 kilometers. They grew through direct
physical collisions with each other.
- Evolution of the planets from protoplanets
- Planetesimals became protoplanets once their masses became great
enough to possess an effective gravitational field. The ability
of protoplanets to obtain more mass was not limited strictly to
their cross sectional areas, as it was for planetesimals. At this
point the protoplanet population rapidly assembled into the solar
system as we essentially know it today.
- The sun initiates thermonuclear fusion. Solar wind and radiation
swept out the remaining gaseous materials from the nebular disk.
- The inner planets became heated and melted. Their primordial
atmospheres were lost. Outgassing from these bodies through volcanic
eruptions eventually created secondary atmospheres. The Jovian
planets because of their great masses retained their primeval
atmospheres which are similar to the composition of the present-day